Electrohydraulic Torque Transfer Device with Integrated Clutch and Actuator Unit

ABSTRACT

A power transmission device includes a housing, a rotatable input member and a rotatable output member supported in the housing by a pair of bearings. A friction clutch is operable to selectively transmit a requested magnitude of torque between the input member and the output member. The clutch is axially positioned between the bearings. An actuator is operable to provide an actuation force to the friction clutch to generate the requested magnitude of torque.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/875,185, filed on Dec. 15, 2006. The disclosure of the aboveapplication is incorporated herein by reference.

BACKGROUND

The present disclosure relates generally to a power transmission deviceoperable to selectively transfer torque between first and second sets ofdrivable wheels of a vehicle. More particularly, the present disclosuredescribes a torque transfer device including a clutch integrallyassociated with driving axle components.

Due to increased demand for four-wheel drive vehicles, many powertransmission systems are typically being incorporated into vehicledriveline applications for transferring drive torque to the wheels. Manyvehicles include a power transmission device operably installed betweenthe primary and secondary drivelines. Such power transmission devicesare typically equipped with a torque transfer mechanism for selectivelytransferring drive torque from the primary driveline to the secondarydriveline to establish a four-wheel drive mode of operation. At leastone known torque transfer mechanism includes a dog-type lock-up clutchthat may be selectively engaged for rigidly coupling the secondarydriveline to the primary driveline when the vehicle is operated infour-wheel drive mode. Drive torque is delivered only to the primarydriveline when the lock-up clutch is released and the vehicle operatesin a two-wheel drive mode.

Another type of power transmission device is operable for automaticallydirecting drive torque to the secondary wheels without any input oraction on the part of a vehicle operator. When traction is lost at theprimary wheels, the four-wheel drive mode is entered. Some transfercases are equipped with an electrically-controlled clutch actuatoroperable to regulate the amount of drive torque transferred to asecondary output shaft as a function of changes in vehicle operatingcharacteristics such as vehicle speed, throttle position and steeringangle. Typically, the power transfer device includes a clutch positionedwithin the transfer case housing.

While many power transfer devices are currently used in four-wheel drivevehicles, a need exists to advance the technology and recognize thesystem limitations. For example, the size, weight and packagingrequirements of the power transmission device may make such system costsprohibitive in some four-wheel drive applications.

SUMMARY

A power transmission device includes a housing, a rotatable input memberand a rotatable output member supported in the housing by a pair ofbearings. A friction clutch is operable to selectively transmit arequested magnitude of torque between the input member and the outputmember. The clutch is axially positioned between the bearings. Anactuator is operable to provide an actuation force to the frictionclutch to generate the requested magnitude of torque.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic of an exemplary vehicle equipped with a torquetransfer mechanism constructed in accordance with the teachings of thepresent disclosure;

FIG. 2 is a cross-sectional view of the torque transfer mechanism;

FIG. 3 is another cross-sectional view of the torque transfer mechanism;and

FIG. 4 is a schematic depicting a hydraulic circuit in cooperation withthe torque transfer mechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the disclosure,its application, or uses.

The present disclosure is directed to a power transmission device thatmay be adaptively controlled for modulating the torque transferredbetween a rotatable input member and a rotatable output member. Thetorque transfer mechanism may be useful within motor vehicle drivelinesas a stand-alone device that may be easily incorporated between sectionsof propeller shafts, directly coupled to a driving axle assembly, orother in-line torque coupling applications. Accordingly, while the powertransmission device is hereinafter described in association with aspecific structural embodiment for use in a driveline application, itshould be understood that the arrangement shown and described is merelyexemplary.

With reference to FIG. 1 of the drawings, a drive train 10 for afour-wheel vehicle is shown. Drive train 10 includes a first axleassembly 12, a second axle assembly 14 and a power transmission 16 fordelivering drive torque to the axle assemblies. In the particulararrangement shown, first axle 12 is the front driveline while secondaxle 14 is the rear driveline. Power transmission 16 includes an engine18 and a multi-speed transmission 20 having an integrated frontdifferential unit 22 for driving front wheels 24 via axle shafts 26. Atransfer unit 28 is also driven by transmission 20 for delivering torqueto an input member 29 of a coupling 30 via a driveshaft 32. The inputmember 29 of the coupling 30 is coupled to driveshaft 32 while itsoutput member is coupled to a drive component of a rear differential 36.Second axle assembly 14 also includes a pair of rear wheels 38 connectedto rear differential 36 via rear axle shafts 40.

Drive train 10 is shown to include an electronically-controlled powertransfer system 42 including coupling 30. Power transfer system 42 isoperable to selectively provide drive torque in a two-wheel drive modeor a four-wheel drive mode. In the two-wheel drive mode, torque is nottransferred via coupling 30. Accordingly, 100% of the drive torquedelivered by transmission 20 is provided to front wheels 24. In thefour-wheel drive mode, power is transferred through coupling 30 tosupply torque to rear wheels 38. The power transfer system 42 furtherincludes a controller 50 in communication with vehicle sensors 52 fordetecting dynamic and operational characteristics of the motor vehicle.The controller is operable to control actuation of coupling 30 inresponse to signals from vehicle sensors 52. The controller 50 may beprogrammed with a predetermined target torque split between the firstand second sets of wheels. Alternatively, controller 50 may function todetermine the desired torque to be transferred through coupling 30 viaother methods. Regardless of the method used for determining themagnitude of torque to transfer, controller 50 operates coupling 30 tomaintain the desired torque magnitude.

FIGS. 2-4 depict coupling 30 in greater detail. Coupling 30 includes aninput shaft 70 selectively drivingly coupled to an output shaft orpinion 72 via a friction clutch 74. An input flange 76 is mounted on oneend of input shaft 70 to provide a mounting provision for a drivelinecomponent such as driveshaft 32.

Coupling 30 includes a housing 80 fixed to a rear axle housing 82. Rearaxle housing 82 rotatably supports a differential case 84 of reardifferential 36. A ring gear 86 is fixed to differential case 84. Pinion72 includes a pinion gear 88 integrally formed thereon and positioned inmeshed engagement with ring gear 86. To achieve the appropriate gearmesh, a height setting shim 90 is positioned between housing 80 and rearaxle housing 82.

Pinion 72 is rotatably supported by a pinion head bearing 92 and aninner tail bearing 94. Pinion head bearing 92 is pressed into housing80. A clip 95 retains inner tail bearing 94 within a pocket formedwithin input shaft 70. A nut 97 retains inner tail bearing 94 on pinion72. Input shaft 70 is rotatably supported within housing 80 by an outertail bearing 96. A nut 98 retains outer tail bearing 96 on input shaft70. Axial movement of pinion 72 and input shaft 70 is restricted by thisarrangement.

As previously mentioned, friction clutch 74 may be selectively actuatedto drivingly interconnect input shaft 70 and pinion 72. Friction clutch74 includes a plurality of inner clutch plates 100 fixed for rotationwith pinion 72 via involute splines. A plurality of outer clutch plates102 are fixed for rotation with a drum 104 via another set of involutesplines. Drum 104 is fixed to input shaft 70. A laser welding techniquemay be employed to accomplish this task. Alternatively, the two-pieceassembly of input shaft 70 and drum 104 may be replaced by a one-pieceshaft having splines generated by a shaping operation.

A piston 106 is slidably positioned within a piston cavity 108 formed inhousing 80. Piston 106 may be acted on by a pressurized fluid toselectively apply a clutch actuation force to inner clutch plates 100and outer clutch plates 102 to transfer torque through friction clutch74. A thrust bearing 110 is positioned between piston 106 and frictionclutch 74 to allow relative rotation therebetween.

Input flange 76 is coupled for rotation with input shaft 70 via aninvolute spline. A snap ring 116 axially retains input flange 76 oninput shaft 70. A bushing 118 rotatably supports input flange 76 onpinion 72 allowing relative rotation therebetween. A seal 120 ispositioned to prevent egress of oil and ingress of contamination betweeninput flange 76 and housing 80. A cap 122 and o-ring 124 seal a bore 126extending through input flange 76. A flinger 128 is coupled to inputflange 76 to encourage debris away from seal 120. Bearing preload isachieved by measuring the components and selecting an appropriatelysized spacer 130 against which outer tail bearing 96 is tightened.During normal driving conditions, outer tail bearing 96 rotates andinner tail bearing 94 is static. Inner tail bearing 94 rotates only whenthere is a differential speed between front wheels 24 and rear wheels38.

Furthermore it should be appreciated that friction clutch 74 is axiallypositioned between pinion head bearing 92 and inner tail bearing 94.This configuration provides a number of design benefits. In particular,a minimized packaging envelope is required due to the length of the rearaxle assembly and coupling combination being greatly reduced compared tocompetitive designs. Competitive couplings are typically not integratedinto the rear axle but instead may be bolted to an axle housing thatrotatably supports the pinion. The known axle housings have apredetermined length in order to maintain an adequate spacing betweenthe pinion head bearing and the pinion tail bearing to support thepinion adequately. The present disclosure utilizes the space betweenpinion head bearing 92 and inner tail bearing 94 by positioning frictionclutch 74 at this location. This packaging feat allows a vehiclemanufacturer to utilize the vehicle under body space for otherchallenges such as maximizing fuel tank volume.

Positioning friction clutch 74 between pinion head bearing 92 and innertail bearing 94 encourages maintaining at least a minimum distancebetween pinion head bearing 92 and inner tail bearing 94. It should beappreciated that an increase in gear life, an increase in bearing life,and a decrease in noise generated by the bearings and gear mesh mayresult from increasing the spacing between the pinion bearings.

Coupling 30 also provides a unique bearing loading arrangement. In astandard rear axle equipped with hypoid gearing, a thrust loadencountered by the hypoid pinion reciprocates between drive and over-runmodes of operation. In the drive mode, the thrust of the gear forcesacts in a first direction 132 toward input flange 76. In an over-run orcoast mode, the thrust is in an opposite direction 134. Oftentimes,steep angle tapered roller bearings are required at the pinion head andpinion tail positions to react the reciprocating loads. The pinion headbearing reacts gear thrust loads in the drive mode while the pinion tailbearing reacts the thrust loads in the over-run mode of operation.Furthermore, a relatively high pre-load is required between the pinionhead and pinion tail bearings to reduce the likelihood of noise causedby the reciprocating load. A high bearing preload increases drag andtherefore reduces the mechanical efficiency of the power transmissiondevice.

The torque transfer device of the present disclosure provides a solutionto issues arising from the reciprocating loads. When coupling 30transfers torque, a thrust load is generated on input shaft 70 in firstdirection 132 toward input flange 76. The load is transferred throughinner tail bearing 94 and nut 97 into pinion 72. In the drive mode ofoperation, a gear thrust load is generated in pinion 72 also acting infirst direction 132. Accordingly, a net thrust load is in the samedirection 132. This thrust load is reacted through pinion head bearing92 into housing 80.

In the over-run mode of operation, the thrust load generated by frictionclutch 74 continues to act in first direction 132 and is transferred topinion 72 as previously described. However, thrust loads input throughpinion 72 are now in the opposite direction 134. The pinion gear thrustloads generated during the over-run mode are of a lesser magnitude thanthe clutch thrust loads. Therefore, the net thrust load on pinion 72 isin first direction 132 and is reacted into housing 80 through pinionhead bearing 92 as previously described. It should be appreciated thatthe net pinion thrust loads experienced by pinion 72 consistently act infirst direction 132. This predictable loading allows for a reducedpreload in the bearing arrangement which also reduces drag and thereforeincreases mechanical efficiency. Because the thrust loading isuni-directional, higher efficiency bearings may be used at theconstantly rotating outer tail bearing 96 position.

FIG. 4 presents a schematic of a hydraulic circuit 200 in communicationwith coupling 30. Hydraulic circuit 200 includes an accumulator 202 forstoring pressurized hydraulic fluid provided by a hydraulic pump 204driven by an electric motor 206. An inlet 208 of pump 204 is incommunication with a low pressure filter 210. Fluid may be drawn from asump 212 through low pressure filter 210 and pump 204. Highlypressurized fluid exits pump 204 and passes through a high pressurefilter 214. Pressurized fluid continues to flow through a check valve216 to charge accumulator 202. Check valve 216 restricts fluid fromflowing in a reverse direction toward pump 204.

A pressure switch 218 controls motor 206 and pump 204 to maintain adesired fluid pressure within accumulator 202. If the pressure withinaccumulator 202 drops below a predetermined value, pressure switch 218closes to cause motor 206 to drive pump 204 and provide pressurizedfluid to accumulator 202. A proportional pressure reducing valve 220 isin communication with the pressurized fluid within accumulator 202.Proportional pressure reducing valve 220 includes a solenoid 222 thatmay be selectively actuated to allow pressurized fluid to act on piston106. In one arrangement, controller 50 provides a pulse width modulatedsignal to solenoid 222 to accurately control the pressure applied topiston 106. As pressure is applied to piston 106, a compressive forceacts on friction clutch 74. The output torque of friction clutch 74 iscontrolled by varying the pressure applied to piston 106 viaproportional pressure reducing valve 220. When solenoid 222 is notactuated, fluid within piston cavity 108 returns to sump 212 and torqueis not transferred through friction clutch 74. A pressure relief valve224 is positioned between accumulator 202 and proportional pressurereducing valve 220 to relieve pressure within accumulator 202 if apredetermined value is exceeded.

Coupling 30 also incorporates a lubrication and actuation system using asingle lubricant from sump 212 to lubricate the rear axle, lubricate andcool friction clutch 74 and also act as the actuation fluid stored inaccumulator 202 acting on piston 106. A GL5 synthetic oil with frictionmodifier additives or an automatic transmission fluid may exhibitdesirable properties for this application. Because a common hydraulicfluid is being used throughout the system, friction clutch 74 mayinclude carbon fiber friction linings. By using a single lubricant, therisk of cross-contamination of lubricants is eliminated.

Motor 206 and pump 204 may also be used to provide a low pressure outputof lubrication spraying onto pinion gear 88 and ring gear 86. A fluidlevel within sump 212 may be maintained below a lower extremity of ringgear 86. Mechanical efficiency of rear axle 14 may be increased due to areduction in churning losses. Alternatively, ring gear 86 may extendinto the fluid contained within sump 212 by a reduced amount compared toa standard rear axle assembly to reduce energy loss.

Furthermore, the foregoing discussion discloses and describes merelyexemplary embodiments of the present invention. One skilled in the artwill readily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationsmay be made therein without department from the spirit and scope of theinvention as defined in the following claims.

1. A power transmission device comprising: a housing; a rotatable inputmember; a rotatable output member supported in the housing by a pair ofbearings; a friction clutch operable to selectively transmit a requestedmagnitude of torque between the input member and the output member, theclutch being axially positioned between the bearings; and an actuatoroperable to provide an actuation force to the friction clutch togenerate the requested magnitude of torque.
 2. The power transmissiondevice of claim 1 wherein the rotatable output member is fixed to apinion gear.
 3. The power transmission device of claim 2 wherein thepinion gear is integrally formed with the output member.
 4. The powertransmission device of claim 3 further including a ring gear beingdriven by the pinion gear, rotatable about an axis and supported withinthe housing, wherein the output member is rotatable about an axisextending substantially perpendicular to the axis of rotation of thering gear.
 5. The power transmission device of claim 1 wherein the inputmember concentrically surrounds the output member.
 6. The powertransmission device of claim 1 wherein the friction clutch includes afirst set of friction plates interleaved with a second set of frictionplates.
 7. The power transmission device of claim 6 wherein the actuatorincludes an axially moveable piston providing the actuation force to thefriction clutch.
 8. The power transmission device of claim 7 wherein theactuator further includes an electric motor driving a pump to supplypressurized fluid to an accumulator, the pressurized fluid selectivelyacting on the piston based on a position of a valve in fluidcommunication with the accumulator.
 9. The power transmission device ofclaim 8 wherein the fluid contacts the rotatable output member forlubrication.
 10. A power transmission device comprising: an axlehousing; a differential assembly having a carrier rotatably supportedwithin the axle housing; a ring gear fixed to the carrier; a rotatablepinion supported by a pair of bearings, the pinion having a pinion gearin driving engagement with the ring gear; a rotatable input member; anda friction clutch operable to selectively transmit a requested magnitudeof torque between the input member and the pinion, the clutch beingaxially positioned between the bearings.
 11. The power transmissiondevice of claim 10 further including a clutch housing mounted to theaxle housing, the input member and the clutch being positioned in theclutch housing.
 12. The power transmission device of claim 11 whereinthe bearings are positioned within the clutch housing.
 13. The powertransmission device of claim 12 wherein one of the bearings encompassesthe pinion and is encompassed by the input member.
 14. The powertransmission device of claim 10 wherein the friction clutch includes afirst set of friction plates interleaved with a second set of frictionplates.
 15. The power transmission device of claim 10 further includingan actuator operable to provide an actuation force to said frictionclutch to generate the requested magnitude of torque.
 16. The powertransmission device of claim 15 wherein the actuator includes an axiallymoveable piston providing the actuation force to the friction clutch,the piston being axially positioned between the bearings.
 17. The powertransmission device of claim 16 wherein the actuator further includes anelectric motor driving a pump to supply pressurized fluid to anaccumulator, the pressurized fluid selectively acting on the pistonbased on a position of a valve in fluid communication with theaccumulator.
 18. The power transmission device of claim 17 wherein thefluid contacts the pinion for lubrication.
 19. The power transmissiondevice of claim 17 further including a pressure switch controlling themotor and pump to maintain a predetermined fluid pressure within theaccumulator.
 20. The power transmission device of claim 11 furtherincluding an input flange at least partially extending outside of theclutch housing, being drivingly coupled to the input member and beingsupported for rotation by the pinion.